The present invention relates to oscilloscope trigger systems, and more particularly to a realtime spectrum trigger system on a realtime oscilloscope.
Realtime oscilloscopes have comprehensive trigger systems to help users obtain stable waveforms for display, quickly capture abnormal behavior, etc. However, these trigger systems are unable to trigger on a periodic signal buried in noise so that subsequent acquisitions of the signal are in time alignment, as shown in FIG. 1. There is no spectrum trigger on realtime oscilloscopes. New realtime spectrum analyzers, such as those manufactured by Tektronix, Inc. of Beaverton, Oreg., have a spectrum trigger that helps to capture frequency events and also display signals in the time domain. However only the magnitude spectrum is considered, while the phase spectrum is not. Phase in the frequency domain corresponds to time delays in the time domain. Time alignment, i.e., phase alignment, is required for the realtime oscilloscope to put multiple acquisitions of a signal in a waveform database.
What is desired is a spectrum trigger system for a realtime oscilloscope that considers both magnitude and phase such that time alignment between successive acquisitions is achieved.